The invention presented herein relates to the composition of zirconium(Zr) alloy having superior corrosion resistance and high strength. In particular, this invention relates to the alloys with superior corrosion resistance and high strength for fuel claddings, spacer grids, and core structural components in light water reactor(LWR) and heavy water reactor (HWR).
Zirconium alloys, in particular Zircaloy-2 and Zircaloy-4, have been widely used as fuel rod cladding and structural elements of nuclear reactor core.
The development of zirconium alloys is illustrated as follows: Zircaloy-1(Sn: 2.5 wt. %, Zr: the balance); Zircaloy-2(Sn: 1.20-1.70 wt. %, Fe: 0.07-0.20 wt. %, Cr: 0.05-1.15 wt. %, Ni: 0.03-0.08 wt. %, O: 900-1500 ppm, Zr: the balance; wherein, Fe+Cr+Ni: 0.16-1.70 wt. %); Zircaloy-3A(Sn: 2.5 wt. %, Fe: 0.25 wt. %, Zr: the balance); Zircaloy-3B(Sn: 0.5 wt. %, Fe: 0.4 wt. %, Zr: the balance); Zircaloy-3C(Sn: 0.5 wt. %, Fe: 0.2 wt. %, Ni: 0.2 wt. %, Zr: the balance); Zircaloy-4(Sn: 1.20-1.70 wt. %, Fe: 0.18-0.24 wt. %, Cr: 0.07-0.13 wt. %, O: 900-1500 ppm, Ni: &lt;0.07 wt. %, Zr: the balance, wherein Fe+Cr: 0.28-0.24 wt. %); and so forth. The above alloys, except for Zircaloy-2 and Zircaloy-4, have not been commercialized due to poor mechanical strength and corrosion resistance in the reactor.
As the operating conditions of nuclear power plants tend to be at high burnup, increased operating temperature, and high pH, Zircaloys could not be utilized as fuel rod cladding. Recently, the extensive and successful research and development have been focused on increasing the corrosion resistance of zirconium alloys.
U.S. Pat. No. 4,649,023 relates to the zirconium alloys, which comprise the following alloy composition, and the manufacturing process of the intermediate and final product thereof.
niobium, in a range of 0.5 to 2.0 wt. %; PA1 tin , up to 1.5 wt. %; PA1 a third alloying element, up to 0.25 wt. %; and PA1 the balance being zirconium. The third alloying element is one of constituent such as iron, chromium, molybdenum, vanadium, copper and tungsten. PA1 tin, in a range of 0.8 to 1.2 wt. %; PA1 iron, in a range of 0.2 to 0.5 wt. % (typically 0.35 wt. %); PA1 chromium, in a range of 0.1 to 0.4 wt. % (typically 0.25 wt. %); PA1 niobium up to 0.6 wt. % (typically up to 0.3 wt. %); PA1 silicon, in a range of 50 to 200 ppm (typically 100 ppm); PA1 oxygen, in a range of 900 to 1800 ppm (typically 1600 ppm); and PA1 the balance being of zirconium. PA1 tin, in a range of 0.2 to 0.9 wt. %; PA1 iron, in a range of 0.18 to 0.6 wt. %; PA1 chromium, in a range of 0.07 to 0.4 wt. %; PA1 niobium, in a range of 0.05 to 0.5 wt. %; PA1 tantalum, in a range of 0.01 to 0.2 wt. %; PA1 vanadium, in a range of 0.05 to 1 wt. %; PA1 molybdenum, in a range of 0.05 to 1 wt. %; and PA1 the balance being of zirconium. PA1 tin, in a range of 0.2 to 1.15 wt. %; PA1 iron, in a range of 0.19 to 0.6 wt. % (typically in a range of 0.19 to 0.24 wt. %); PA1 chromium, in a range of 0.07 to 0.4 wt. % (typically in a range of 0.07 to 0.13 wt. %); PA1 tantalum, in a range of 0.01 to 0.2 wt. %; PA1 niobium, in a range of 0.05 to 0.5 wt. %; PA1 nitrogen, in less than 60 ppm; and PA1 the balance being of zirconium. PA1 Niobium, in a range of 0.5 to 1.5 wt. %; PA1 tin, in a range of 0.9 to 1.5 wt. %; PA1 iron, in a range of 0.3 to 0.6 wt. %; PA1 chromium, in a range of 0.005 to 0.2 wt. %; PA1 carbon, in a range of 0.005 to 0.04 wt. %; PA1 oxygen, in a range of 0.05 to 0.15 wt. %; PA1 silicon, in a range of 0.005 to 0.15 wt. %; and PA1 the balance being of zirconium.
This alloy is characterized to have the a microstructure with homogeneously dispersed fine precipitates of less than about 800 .ANG.. This was included to improve corrosion resistance in high temperature steam by controlling its microstructure.
The zirconium alloy with similar corrosion resistance to that in U.S. Pat. No. 4,649,023 is suggested in U.S. Pat. Nos. 5,112,573 and 5,230,758. This alloy includes niobium in a range of 0.5 to 2.0 wt. %, tin in a range of 0.7 to 1.5 wt. %, iron in a range of 0.07 to 0.14 wt. %, at least one of nickel and chromium in a range of 0.03 to 0.14 wt. %, and carbon up to 220 ppm, wherein the total amount of nickel and chromium is at least 0.12 wt. %. And, corrosion resistance is improved by chromium and nickel in a range of 0.03 to 0.08 wt. %.
U.S. Pat. No. 4,879,093 discloses improvement of corrosion resistance and ductility by adding up to 0.6 wt. % of niobium or up to 0.1 wt. % of molybdenum in the Zircaloy. The amount of oxygen was in a range of 1000 to 1600 ppm, and the second-phase was in a range of 1200 to 1800 .ANG..
The zirconium alloy of U.S. Pat. No. 5,080,861, the invention with improved corrosion resistance in the reactor core of nuclear power plant, includes up to 0.6 wt. % of niobium, up to 0.2 wt. % of antimony, up to 0.2 wt. % of tellurium, tin in a range of 0.5 to 1.0 wt. %, iron in a range of 0.8 to 0.24 wt. %, chromium in a range of 0.07 to 0.13 wt. %, oxygen in a range of 900 to 2000 ppm, less than 70 ppm of nickel, and less than 200 ppm of carbon. This alloy consists of .alpha.-phase in which the second phase in the size of 1200 to 1800 .ANG. is somewhat precipitated, and may include up to 0.2 wt. % of silicon instead of tellurium and arsenic(As).
The improved zirconium alloy based on the above patent, U.S. Pat. No. 5,080,861, was additionally issued in U.S. Pat. No. 5,211,774. This alloy, which has a similar alloy composition to that in the above patent, has improved properties in ductility, creep strength and corrosion resistance because of the stabilized .alpha.-phase. It comprises an alloying composition as follows:
In this alloy, silicon decreases hydrogen uptake, and increases corrosion resistance.
U.S. Pat. No. 5,244,514 also discloses the zirconium alloy having stabilized precipitates, which are formed when the alloy is exposed to thermal neutron as well as high temperatures. This alloy includes a smaller amount of tin as compared with the former existing Zircaloys, and has a low capture cross section of thermal neutrons, superior corrosion resistance, low hydrogen uptake, good workability and improved creep resistance. This alloy is composed of vanadium up to 1.0 wt. %, up to 1.0 wt. % of niobium, up to 0.2 wt. % of antimony and tellurium, up to 0.5 wt. % of tin, iron in a range of 0.2 to 0.5 wt. %, chromium in a range of 0.1 to 0.4 wt. %, silicon in a range of 50 to 200 ppm, up to 2200 ppm of oxygen, and the balance being of zirconium. The vanadium compound(ZrV.sub.2), which is the precipitate formed in this alloy provides good creep resistance, low hydrogen uptake, and stability in neutron flux and in high burn-up.
U.S. Pat. No. 4,963,323 discloses the material for fuel cladding with improved corrosion resistance by adjusting the composition of the former existing Zircaloy-4. That is, the amount of tin was decreased and noibium was added as compensation, and the amount of nitrogen was controlled to less than 60 ppm in this alloy. Therefore, the alloy included tin in a range of 0.2 to 1.15 wt. %, iron in a range of 0.19 to 0.6 wt. % (typically 0.19 to 0.24 wt. %), chromium in a range of 0.07 to 0.4 wt. % (typically in a range of 0.07 to 0.4 wt. %), niobium in a range of 0.05 to 0.5 wt. %, and less than 60 ppm of nitrogen.
U.S. Pat. No. 5,017,336 discloses the improved Zircaloy-4 with niobium, tantalum(Ta), vanadium, and molybdenum, and this alloy comprises an alloy composition as follows:
U.S. Pat. No. 5,196,163 discloses the improved zirconium alloy containing tantalum as well as the usual components which are tin, iron and chromium, but also with tantalum, and selectively, niobium, and the alloy composition is as follows:
U.S. Pat. No. 5,560,790 discloses the zirconium alloy, which comprises the following alloy composition.
In this patent, the distance between the precipitates, Zr(Nb, Fe)2, Zr(Fe, Cr, Nb), and (Zr, Nb)3Fe, was limited to the range of 0.20 to 0.40 .mu.m, and the volume of the precipitate containing iron was limited to 60% of the total volume of precipitate.
CA 2,082,691 describes the zirconium alloy maintaining ductility to the degree of sponge zirconium and corrosion resistance improved by adding bismuth in a range of 0.1 to 0.5 wt. % and niobium in a range of 0.1 to 0.5 wt. % (typically in a range of 0.1 to 0.3 wt. %).
The zirconium alloys are suitable for material used in fuel rod cladding because of the small capture cross section of thermal neutron and relatively good corrosion resistance at high temperature. The zirconium alloy for the present fuel rod cladding is Zircaloys with tin, iron, chromium, and nickel.
However, considering the circumstances of the extended and high burn-up fuel, the use of Zircaloys as material for fuel rod cladding becomes limited due to enhanced corrosion and irradiation creep. Therefore, the development of an advanced zirconium alloy with high strength and corrosion resistance has been required.
We, the inventors of this invention, successfully developed a zirconium alloy with higher strength and superior corrosion resistance than the former existing Zircaloys through making changes in the kinds and amounts of alloying elements.